Method for extruding profiled sections of expanded thermo plastic material having an integral skin

ABSTRACT

This invention relates to the manufacture by extrusion profiled products of expanded plastic material. An expansible plastic composition is extruded through an annular die opening into a cooled shaper having the same cross-section as the desired product, in such a manner that a high-density, rigid skin is formed on the extrudate and the composition expands inwardly within the shaper.

United States Patent [1 1 Boutillier METHOD FOR EXTRUDING PROFILEDSECTIONS OF EXPANDED THERMO PLASTIC MATERIAL HAVING AN INTEGRAL SKINPierre Emile Boutillier, Colombes, France [75] Inventor:

[73] Assignee: Societe Anonyme Ugine Kuhlmann,

Paris, France Filed: Mar. 20, 1969 Appl. No.: 808,760

Related U.S. Application Data Continuation-impart of Ser. No. 664,738,Aug 31, 1967, abandoned.

[30] Foreign Application Priority Data Oct. 9, 1973 [56] ReferencesCited UNITED STATES PATENTS 3,300,554 1/1967 Bachus 264/47 3,413,38811/1968 Lux et al.... 264/46 3,431,164 3/1969 Gilbert 264/48 X 3,363,034l/l968 Noland et a1. 264/48 3,413,387 l1/l968 Ohsol 264/46 3,431,1633/1969 Gilbert 161/161 3,387,067 6/1968 McCurdy 264/53 PrimaryExaminer-Philip E. Anderson Attorney-Brumbaugh, Graves, Donohue &Raymond [57] ABSTRACT 15 Claims, 16 Drawing Figures METHOD FOR EXTRUDINGPROFILED SECTIONS OF EXPANDED THERMO PLASTIC MATERIAL HAVING AN INTEGRALSKIN This is a continuation-in-part of my prior application Ser. No664,738 filed Aug. 31, 1967, now abandoned.

The extrusion of expansible plastic materials through a die gives ariseto difficulties because the expansible material, whichcontains anexpanding agent capable of forming a very large number of small cavitiesinside the mass, to give an end product in the form of a rigid,semi-rigid, or flexible foam, must be only slightly expanded, if at all,when it is forced through the die, if a regular flow is to be obtained.Moreover, the section of the profiled product obtained by expansion inthe open atmosphere cannot be accurately predicted, and the cellularstructure of the profile obtained may not be regular.

When the material is allowed to expand freely upon leaving the die, thecomputation of the shape of the latter is highly complicated, because itis found that the section of the die cannot be exactly homothetic tothat of the profiled product to be obtained, and has to be determinedexperimentally in each case. Thus, for example, to obtain a profiledproduct of square section, it is necessary to give the die a concavecurvilinear square section of smaller area, the reduction in areavarying with the final section of the product, the composition of theextruded material, and the conditions of extrusion. However even with acorrectly shaped die irregularities of shape still occur.

One known method of surmounting these difficulties depends on the use,immediately downstream of the die, of a shaper having an inside sectionidentical to the section of the profiled product required, in which theexpansion takes place, and which contains and regularizes the expansionof the extruded material to the desired constant shape and dimensions.

Nevertheless, the use of a shaper of this type, which is conventional inthe extrusion of non-expansible plastic materials, encounters greatdifficulties in the case of expansible material. It is not possible touse a shaper with a cross-section identical in shape and dimensions withthat of the die, because the material cannot expand therein, and thedensity of the profiled expanded product leaving the shaper would bevery close to the real density of the unexpanded product. In addition,the pressure of the gases released by the expanding agent tends to forcethe profiled product against the walls of the shaper, and the expulsionof the profiled product from the shaper has to be effected by the worm.The periphery of the product is cooled by contact with the wall of theshaper, while the core remains hot. Thus the core, which is cooled bycontact with the wall of the shaper, receives a concentration ofmaterial supplied by the worm, which hinders still further anypossibility of expansion.

Attempts have been made to overcome these obstacles by using a diehaving a section smaller than that of the profiled product to beobtained, and therefore than the section of the shaper, in the beliefthat the larger section of the latter would produce the desired resultby enabling the material leaving the die to expand freely. In practice,however, after expansion a fairly hard crust is formed on contact withthe wall of the shaper because of the cooling previously mentioned, andthis crust is forced against the wall by the expansion pressure, Thefrictional forces are then so great that a drawing caterpillar cannotwithdraw the profiled product from the shaper without breaking the crustand consequently stretching the central portion of the profiled product,which has remained hot. At the same time the extrusion worm continues tofeed material to the core of the profiled product, and the entireextrusion device may then become blocked. In addition, between themoment when the profiled product leaves the die and the moment when itis forced by expansion against the walls of the shaper, incipientfractures are frequently formed on its surface, which reduce itsmechanical strength. This arrangement with a die of smaller section thanthat of the shaper can be used in practice only with profiled productsof very small section, or with very low delivery rates, where thecooling is sufficiently rapid to enable the outer crust to besufficiently strong to permit the extraction of the profiled productwithout the above mentioned drawbacks.

In certain cases it is desirable to obtain composite, profiled sectionscomprising an outer sheath made from thermoplastic and/or elastomercomposition, and a cellular internal structure, the composition of whichmay be the same as, or different from that forming the outer skin orsheath.

Usually, when it is desired to produce such composite sections it isnecessary to produce the sheath by extrusion in a first step, and thento fill said sheath in a second step with the cellular material. Thisproduction, which is not continuous, has in addition the disadvantage ofpermitting the manufacture of composite sections of a limited lengthonly.

Composite sections can also be manufactured with the aid of a cross-headcomprising coaxial die sections and connected to two extruders. One ofthe said extruders feeds the outer passage of said cross-head with amaterial intended to produce the outer sheath or skin byconstraining thematerial to flow through an opening having substantially the shape andarea of the sheath to be obtained, the said opening being defined on theoutside by the so-called die and on the inside by a so-called mandreland located axially of the sheath to be produced. The second extruder isconnected to an opening I which is located in the axis of the mandreland the outlet of which leads into the sheath.

With such an apparatus the material is certainly expanded on leaving thepassage situated in the axis of the mandrel and the sheath beingextruded is filled with a cellular material, but only when the innersection of the sheath is of a simple shape, for example circular orsquare. Even in this case, for example with a sheath of squarecross-section, tests have shown thatin order to obtain good filling ofsaid square cross-section the opening located in the axis of the mandreland through which an expansible material is extruded to form the innercentral part of the desired product should have an outlet cross-sectionof concave curvilinear square shape, with an area which is obviouslymuch smaller than the inner surface of the sheath. In other words, inorder to achieve a correct filling of the sheath of a passage extrusionopening should be used the outlet crosssection and shape of which can bedetermined only experimentally.

Such a method is still further limited by the degree of expansion of thematerial intended to form the cellular structure, because even in thecase of the filling of a sheath of simple cross-section, for examplesquare or circular but of fairly large dimensions, it is practicallyimpossible to achieve close contact between the inner surface of thesheath being extruded and the outer surface of the cellular materialundergoing expansion, which leads to the production of compositesections having mediocre mechanical properties.

An object of this invention is the easy manufacture of solid or hollowprofiled products of expanded plastic material and of any section asregards shape and dimensions, which have a perfectly defined, constantprofile over their entire length.

Another object of the invention is to produce solid or hollow sectionsof expanded plastic materials which have a smooth, glossy surface due totheformation of a continuous skin, substantially free from faults, bothon their outer surface and, in the case of tubular hollow sections alsoon their inside surface.

Another object of the invention is to provide these sections with aregular cellular structure resulting in good mechanical properties.

Yet another object of the invention is to obtain highly improvedmechanical properties for these sections by means of the aforesaidcontinuous skin.

Still another object of the invention is to provide a method for theobtention of composite sections comprising an outer sheath made fromthermoplastic and- /or elastomer composition, and a cellular internalstructure also made from a thermoplastic and/or elastomer compositionwhich may be the same as, or different from that forming said outersheath, and in which a perfect and continuous bonding is created betweenthe outer sheath and the inner cellular material.

These and other objects of the invention will become apparent in thecourse of the following description.

These objects are achieved according to the invention, by a method whichcomprises extruding expansible plastic material in an at least partlyunexpanded state into an elongated shaper open at both ends dis posedsubstantially coaxially with the die and having an inlet sectionsubstantially equal in area to the die and an outlet section identicalto that of the product required, and providing a cavity inside thematerial during extrusion through the die, whereby the extruded materialexpands inwards so as to' at least partially till the cavity. Theformulation of thecomposition'to be extruded, as regards its expansionproperties, and'the conditions of the extrusion, the section of theinternal cavity in the material during the expansion, and the length andprofile of the shaper are determined so that the extruded materialduringits passage through the shaper undergoes the desired inwardsexpansion.

By the expansion die section" is understood the cross-section at theoutlet of the die, without taking into account the existence of thecavity formed inside the extruded composition.

When the material leaves the die and comes into contact with a shaperthe temperature of which is below the softening point of the polymer,the latter rapidly forms a hard layer in contact with the wall of theshaper. During the performance of the invention, the expansion takesplace fundamentally from the outside to inside, the material beingpressed against the inside wall of the shaper. The section can thusslide in the shaper, firstly because the thrust of the worm istransmitted to the outer layers of the extruded material, which israpidly solidified on contact with the shaper, and secondly becausethere is no ramming of material into the shaper. A drawing caterpillarmay be used if desired, without any risk of breaking of the skin formedagainst the wall of the shaper, or any inequality caused by stretching.However, it is advantageous to make the maximum use of the thrustapplied by the worms of the extruder in order to advance the extrudatethrough the shaper, and for this reason it is preferable to give the dieand the shaper the same cross-section, so that the thrust of the wormcan be transmitted to the hard outer layer.

it will be understood that it is thus possible to obtain extrudedproducts of any section which have constant cross-sectional dimensionsand a smooth surface. The cavity initially formed in the central portionof the section during extrusion may be filled completely or if preferredonly partially by the expansion of the material.

The calculation of the various parameters determining the performance ofthe method according to the invention is very simple to anyone skilledin the art. Once the formulation of the expansible plastic compositionto-be extruded has been settled, this calculation is restricted to theselection of conditions by calculation and/or experimentation; theseare, principally, the selection of the extrusion speed and temperature,the shape and dimensions of the hollow space inside the extrudedproduct, (i.e. of the mandrel disposed in the die) and the length of theshaper so that on leaving the latter the material will have attained thedesired dimen- SlOllS.

Supplementary regulation of the expansion, also making it possible tocontrol the thickness of the outer skin formed on the extruded material,may be achieved by raising or lowering the temperature of the die,mandrel, or walls of the shaper. This may be easily done, for example,by regulation of the electric heating and/or the circulation of heatingand/or cooling fluid in these different parts.

As has been stated, the cavity originally formed in the centre of theextruded material need not be completely filled by expansion, and may beretained when the mechanical characteristics required in the finalextruded products make this possible or desirable.

As has been indicated above, the invention makes it possible to obtainextruded products of all sections, particularly solid or massivesections, possibly containing the residual cavity referred to above, andalso tubular products of any external and internal dimensions; in thelatter case the free surfaces both on the outside and on the inside havethe exceptionally advantageous qualities which have already beenmentioned.

Tubular sections of this type may also be obtained.

It is likewise possible to obtain alternately solid and hollow sectionsby extruding an expansible plastic material by the method according tothe invention. As the extruded product is continuously pulled out of theshaper, and the extrusion parameters are cyclicly varied to givealternate hollow and solid lengths of extruded product. Thus, during afirst period of time the pulling speed may be such as to give a lengthof solid cross-section, then for a second period of time the speed maybe increased to give a hollow length of extruded product, in which theexpansion of the material is insufficient to fill the internal cavity.This cycle may be repeated or varied as often as desired.

it will be understood that by alternating a short period of extrusion atthe desired pulling speed so as to obtain a solid length of extrudedproduct, and then a longer period of extrusion at a higher pulling speedgiving rise to the production of a hollow length, and then a furthershort period of extrusion at the first speed mentioned, a hollow lengthof extruded product closed at both ends will be formed. If extrudedproducts having a rectangular section are produced in this manner,products similar to hollow bricks are obtained. By continuing thesealternations of speed, either regularly or irregularly, it is possibleto obtain a continuous hollow length of product having solid portionsforming braces at regular or irregular intervals. The total apparentdensity of the lengths of product thus obtained is reduced, whilemechanical strength properties are obtained. At the same time, theiracoustic and thermal properties are improved because of the gasimprisoned therein.

As has been mentioned above, the thickness of the solid skin may bemodified by adjusting the extrusion parameters, particularly thetemperatures of the die, mandrel, and shaper. This thickness is reducedwhen these temperatures are raised. At the limit, there is no longer asmooth solid surface at all.

When it is desired to obtain a solid outer sheath closely covering aninner part of expanded material, the composition intended to form saidouter sheath is extruded through a first annular die substantiallyconforming the shape of the desired sheath, in close vicinity of theinner wall or walls of the inlet part of the shaper, whereas theexpansible composition is extruded as above disclosed through adie-section arranged inwardly and substantially coaxially with respectto said first die.

The accompanying drawings illustrate diagramatically, by way of example,various forms of construction of apparatus for'carrying out theinvention. In these drawings:

FIG. 1 is a longitudinal sectional view of the end of an extrusionmachine with its die, and of a shaper for extruding a round bar.

FIG. 2 is a cross-sectional view along line IIII in FIG. 1.

FIG. 3 is a cross-sectional view of the shaper illustrated in FIG. 1.

FIGS. 4 and 5 are cross-sectional views of a die for producing aT-section and of the corresponding shaper, respectively.

FIG. 6 is a longitudinal sectional view similar to that shown in FIG. 1,of an apparatus for producing a hol-' low section.

FIGS. 7 and 8 are cross-sectional views of the die and shaper,respectively, of the apparatus illustrated in FIG. 6, respectively alonglines VIIVII and VIII-VIII in FIG. 6. I

FIG. 9 is a cross-sectional view ofa first embodiment of a die forextruding a board of rectangular section.

FIGS. 10 and 11 are cross-sectional views of another embodiment ofa diefor producing a board having a biconcave lens cross-section and of thecorresponding shaper, respectively.

FIG. 12 illustrates diagrammatically in longitudinal section an exampleof equipment for carrying out the invention, in which the section ispulled at the outlet of the shaper, for the purpose of producingalternatively solid and hollow sections.

FIG. 13 is a longitudinal sectional view of an alternately solid andhollow section obtained in accordance with the invention.

FIG. 14 is a longitudinal sectional view of an extru-. sion head and ofa shaper for the extrusion of a composite section according to theinvention.

FIG. 15 is a similar view of a modification of the apparatus illustratedin FIG. 14, intended in this case for extruding a reinforced compositesection.

FIG. 16 is a cross-section of a reinforced section obtained with theapparatus illustrated in FIG. 15.

As illustrated in FIGS. 1 to 3, apparatus which may be used for carryingout the invention comprises an extrusion machine of any usual type,designated generally by the reference 1, and comprising a body 2, anextrusion worm 3, of which only the end is shown, and a die 4, which inthe example selected is of circular section. A mandrel 5,'held in theaxis of the die by three supports 6 spaced at 120, is arranged in thedie. Against the outlet of the die is a shaper 7, constituted by atubular sleeve forming a'cylindrical guide having an inside wall 8,which may be smooth, of the same cross-section as the die 4 The shaper 7has a double wall forming a heat-controlling jacket 9 provided withconnections 10 and 11 enabling a temperature-controlling fluid to becirculated therein.

The expansible plastics composition 12 to be extruded, for examplepolystyrene containing an expanding agent and the usual additives, isintroduced into the extrusion machine and driven by the worm 3 throughthe die 4 into the space between'the mandrel 5 and the inside wall ofsaid die. The extrusion-conditions are such that the expansiblecomposition is only slightly expanded or not expanded at all as itpasses into the die but startsto expand immediately on leaving orshortly before leaving the latter. At the outlet of the die the materialundergoing expansion is delivered through the shaper 7, the outlet ofwhich is kept at a temperature lower than the gelling point of theextruded composition. On contact with the inside wall 8 of the shaperthere is thus formeda hard layer 13 of plastic material, the thicknessof which is not always as great as is shown in the drawing for the sakeof clarity.

The expansion of the plastics material under the action of the expandingagent takes place inwardly filling the cavity 14 formed in the centre ofthe material by the mandrel 5. The shape and the dimensions of thelatter and the length of the passage 8 in'the shaper are calculated sothat, taking into account the formulation of the composition to beextruded and the various conditions of extrusion, the inwards expansionof the material in the shaper leads to the at least partial filling ofthe void 14.

At the outlet of the shaper there is thus obtained a cylindrical bar 15of expanded plastics material having a constant cross-section, which isthe same as the crosssection of the outlet of the shaper. This bar has asmooth surface, if the inside wall of the shaper is itself smooth, andif the extrusion parameters, particularly the temperature of themandrel, die and shaper, are judiciously selected. The bar is pushedthrough the shaper by the delivery of more expansible material by theworm 3, the pressure resulting from this delivery being applied directlyto the outer layer 13. If this pressure is found insufficient to effectthe necessary propulsion, use may be made of a drawing caterpillar (notshown) of any type which is connected to the end of the bar beingextruded.

The temperature regulating jacket 9 of the shaper 7 enables thetemperature of the shaper to be adjusted;

this temperature, together with those in the extrusion machine and inthe die and the extrusion speed, constitute the main parameters of theextrusion conditions which, at the same time as the shape and dimensionsof the mandrel 5, must be determined by calculation and- /orexperimentation so that the desired result, namely the expansion of thematerial filling the central void 14 partially or totally, is obtained.

It will be realised that by the same principles it will be possible toobtain extruded products of absolutely any cross-section, the latterdepending solely on the inside cross-section of the die and of theshaper.

Thus, FIGS. 4 and illustrate a die and a shaper intended for producing aT-section. In this example the die 24 has an inside section identical tothat of the final product to be obtained and insaid die there is engageda mandrel 25 of T-shaped section which is held axially in the die bysupports 26 situated at the rear portion of the mandrel, similarly tothe supports 6 of the mandrel 5 illustrated in FIG. 1. The area of thesection of the mandrel 25 is determined in dependence on all the ex,

trusion conditions and the formulation of the extruded composition, soas to ensure that the expansion of the latter will take place inwardly,as has already been described with relation to FIGS. 1 to 3.

In order to facilitate the expansion of the material and the filling ofthe cavity caused by the mandrel in the die 24, a slight reducedpressure may if desired be produced in said void. This may for examplebe achieved, as illustrated in FIG. 4, by means ofa passage 36 providedlongitudinally in the mandrel 25 and lead-v ing to the front face of thelatter, said passage 36 communicating through a passage 37 transverselythrough the mandrel, one of the supports 26 and the wall of theextrusion machine I, and capable of being connected to a vacuum source.Provision may also be made to provide a slight reduced pressure alongthe inside wall 28 of the shaper, for example by providing passages 38of very small diameter through the wall of said shaper, as illustratedin FIG. 5, said passages being connected by any means (not illustrated)to a source of vacuum, which may be the same as that utilised to providea reduced pressure in the centre of the material. This last arrangementis not always found necessary because the expansion of the material,while taking place from the exterior to the interior, also tends toapply the outer crust of the section being formed against the insidewall of the shaper. in addition, it is obvious that the arrangementswhich have just been described regarding the creation of a reducedpressure on the inside or outside of the section being formed are notspecific to the shape of the section forming the object of FIGS. 4 and5.

The invention also makes it possible'to produce hollow or tubularsections of any shape, as illustrated by way of example in FIGS. 6 to 8.As illustrated inthese Figures, the apparatus for performing theinvention, for

the purpose of obtaining a tubular section, comprises, I

profiled product. In the annular die thus formed a likewise annularmandrel 45 is supported by feet 46, its

shape and dimensions being predetermined as indicated in connection withthe mandrel 5 illustrated in FIG. 1 and the mandrel 25 illustrated inFIG. 4. A shaper 47 having an outside wall 47a and an inside 47brespectively reproducing the contours of the walls 44a and 44b of thedie is disposed directly at the outlet of the latter, the outer wall 47aand inner wall 47b at the shaper being held in position for example byfastening on the die with the aid of flanges or other means (notillustrated).

During extrusion with the aid of the apparatus just described, thematerial is delivered by the worm 3 of the extruding machine through thedie 44, into the spaces between the mandrel 45 and the outer wall 44a Ion the one hand and the inner wall 44b of said die on the other hand,and is then fed into the shaper 47. The presence of the mandrel 45produces in the mass of extruded material penetrating into the shaper 47an annular cavity corresponding to that of the mandrel, said cavitybeing filled by the expansion of the material which takes place towardsthe interior of the space contained between the walls 47a and 47b of theshaper, along which walls the material solidifies on leaving the die,forming hard layers 53a and 53b (FIG. 8). At the outlet of the shaperthere is thus obtained a tubular product having the cross-sectionillustrated at FIG. 8, this cross-section being constant and regularlyreproducing that of the passage in the shaper, while both the outersurface and the inner surface of the extruded product may be smooth.

It is obvious that, as in the preceding cases, the shaper 47 maylikewise be surrounded by a temperature controlling jacket, and passagesmay be provided to produce a reduced pressure both in front of themandrel 45 and along the surface of the partitions in the shaper 47.

In certain cases the mandrel disposed in the die in order to form in theextruded material the cavity intended to be filled through the inwardsexpansion of the material, instead of being held axially in the die byproviding a free space of predetermined cross-sectional dimensions allaround said mandrel in the actual die, maybe connected to the wall ofthe latter, forming a partition dividing the die into two or moreseparate passages. Thus, for the extrusion of a profiled product in theform of a board of rectangular section, it is possible, as illustratedin FIG. 9, to use in a die 64, which has a cross-section identical tothat of the board to be obtained, a mandrel 65 of flattened shape whichis held axially in the die with the aid of supports 66, similar to thesupports 6, 26, or 46 in the preceding Figures. Alternatively, asillustrated in FIGS. 10 and 11 for the extrusion of a board having, forexample, a different cross-section from that obtained with the aid ofthe die illustrated in FIG. 9 and having the shape of a biconcave lens,it is possible to use a die 74, the cross-section of which is the sameas that of the extruded product to be obtained and is divided into twoby a mandrel 75, which is in the form of a partition integral with theedges of the die. The material extruded through a die of this type intothe shaper 77 having the same section as the board to be obtainedundergoes in said shaper an inwards expansion resulting in the closingof the transverse void formed by the mandrel 75, forming partitions, theouter crust being formed continuously over the entire extent of theinside wall of the shaper 77.

The equipment illustrated in FIG. 12 comprises, in the same manner ashas already been described with reference to FIGS. 1 to 3, an extruder 1with its body 2, its extrusion worm 3, and its die 4, in the axis ofwhich is a mandrel 5 to form a central cavity 14 in the extruded producton leaving the die, and on the other hand the shaper 7 consisting ofatubular sleeve forming a cylindrical guide 8 having a smooth inside walland of the same section as the die 4 and comprising a double wallforming a heat controlling jacket 9 provided with connections 10 and 11,which enable a temperature regulating fluid to be circulated therein.

A drawing caterpillar 80, operated by the usual drive mans (notillustrated) makes it possible to draw the section in order to extractit from the shaper 7, which is here followed by a cooling tank 81through which the section 15 passes. As has been described previously,the composition 12 of expansible plastics material which is to beextruded, for example polystyrene containing an expanding agent and theusual additives, is introduced into the extrusion machine and deliveredby the worm 3 of the latter through the die into the space providedbetween the mandrel 5 and the inside wall of said die, the extrusionconditions being such that said material is only slightly expanded ornot expanded at all when it passes into the die but starts its expansionimmediately on leaving or shortly before leaving the latter. At theoutlet of the die the material undergoing expansion is delivered throughthe shaper 7, the outlet of which is kept at a temperature lower thanthe gelling point of the extruded composition. On contact with theinside wall 8 of the shaper, there is thus formed a hard layer 13 ofplastic material, the thickness of which is not always as great as isillustrated in the drawing for the sake of clarity.

The expansion of the plastics material under the action of the expandingagent takes place from the exterior to interior of the mass deliveredinto the shaper,

filling the cavity 14 formed at the centre of the material through thepresence of the mandrel 5.

By regulating the speed of drawing by the caterpillar 80 so that, takinginto account the nature of the extruded composition and the otherextrusion parameters, the expansion of the material, which tends to takeplace inwardly, completely fills the void 14, a section is firstobtained which comprises a hard, compact outer layer 13, which may besmooth, and a solid cellular interior 15a. If after a certain extrusiontime the drawing speed is increased so that there is no time for theexpansion to take place as far as the axis of the section, the latterwill not filled but will have a hollow internal zone 15b, Return to thefirst drawing speed will then produce a further length of solid section,and so on. An extruded product having alternately solid and hollowsections is shown in FIG. 13.

As illustrated diagrammaticaly in FIG. 14, the apparatus for extruding acomposite section comprises an extrusion head of the well-knowncross-head type, which is designated generally by the reference 101 anda shaper 102.

The cross-head comprises a body 103 in which there is provided an axialpassage 104 having at its downstream end a portion 105 of largerdiameter, in which is arranged a die 106 of circular cross-section, theouter diameter of which is smaller than the inside diameter of saidportion 105, said die being supported on the hand laterally by screws107 passing through the body 103 of the head and regularly distributedaround the latter, four or six such screws being for example provided,and on the other hand supported by an annular block 108 held on thefront face of the body 103 of head 101 by screws 109. A sleeve 110 isintroduced into the axial passage 104 of the body 103 of the head, thefront portion 111 of said sleeve having a diameter smaller than that ofthe passage 104, so as to provide inside the body 103 an annular channel1 12 for the passage of plastic compositions in the fused state, whichis driven into said annular channel by a first worm extruder'(not shown)fitted to a connection 113 commucating with a radial channel 114 formedin the body 103 and leading into annular channel 112. The front end 115of sleeve 110 cooperates with die 106 to form an annular die section116, through which the plastics material coming from the first extruderis extruded. The radial dimension or die section 116, which determinesthe thickness of the product extruded through said die section, may bemade uniform over the entire periphery by adjusting the position of die106 with the aid of screws 107 after slackening annular block 108, whichis tightened again after this adjustment.

Near its rear end the sleeve 110 has a portion 117 of smaller diameter,in which is held a mandrel 118 provided with an inner cavity 119 andextending axially over the entire length of the head. The rear portion120 of the mandrel 118, the outer diameter of which is greater than thatof the remainder of its length, is held against a shoulder 121 formed byportion 117 of sleeve 110 by a cover screwed on the rear end ofthe body103 of head 101, said cover likewise holding the sleeve 110 in said body103.

Between said mandrel 118 and the front portion of the sleeve 110 isprovided a second annular channel 122 for the passage of an expansibleplastics material composition in the fused state, which is forced intosaid annular channel by a second worm extruder (not shown) fitted to aconnection 123, communicating with a radial channel 124 formed in body103 and followed by a channel 125 leading into annular channel 122.

The front end 115 of sleeve 110 forms, in coopera- I tion with mandrel118, an annular die section 126 through which the expansible plasticsmaterial composition coming from the second extruder is extruded.

A heating liquid fed through pipe connections 127 and 128 may becirculated in the cavity 1 19 of mandrel 118 in order to maintain a wellcontrolled determined temperature in said mandrel and consequently inthe expansible composition passing through annular channel 122, whilemeans such as an electric resistor 129 surrounding the front end of thecross-head 101, are provided to ensure that the desired temperature ofthe composition flowing through annular channel 112 is maintained.

The shaper 102 arranged in line with the cross-head 101 has an internalcylindrical wall 131 the diameter of which corresponds with that of die106. This wall is pierced with a large number of capillary apertures 132through which the axial cylindrical passage of the shaper communicateswith an annular chamber 133 connected by a pipe 134 to a vacuum pump(not shown). Chamber 133 is itself surrounded by a jacket 135 providedwith pipes 136 and 137 for the circulation of a cooling fluid, forexample water.

A water cooling tank and a drawing crawler of conventional type (notshown) are provided downstream of the shaper.

The plastic composition extruded through channel 112 and the extrusionopening 116 forms a sheath 138, which is applied against the inner wall131 of the shaper under the effect of the vacuum created in the annularchamber 133. The extruded expansible composition delivered throughannular channel 122 and die section 126 is injected inside said sheath138, in which its expansion takes place inwardly as herein abovedescribed. A section comprising an outer sheath 138 and an innercellular portion 139 is thus obtained.

The apparatus illustrated in FIG. 15 generally comprises the same partsas that in FIG. 14. Saidl parts of corresponding to those in FIG. 14 aredesignated by the same reference numerals, with the addition of 100, andwill be specifically described only to the extent to which they aremodified as compared with the previously described apparatus. Theselected example relates to the extrusion of a rectangularcross-section, as illustrated in FIG. 16, comprising acentral metal coreor reinforcement 240 surrounded by a layer of cellular plastic material241, which in turn is covered by a sheath of compact plastic material242.

For this purpose the die 206, the front end215 of the sleeve 210, andthe mandrel 218 have rectangular cross-sections of dimensionscorresponding respectively to the desired result.

The sleeve 210 is here provided with an annular cavity 243 extendingthrough practically its entire length and containing, on its face remotefrom the longitudinal axis, a heat insulating covering 244, for exampleof asbestos, and inside said covering, at the front portion of thesleeve, heating resistors 245 fed by leads 246 which pass out at therear portion of the sleeve and to the outside of the body 203 of headthrough achannel 247 provided for this purpose.

A bore 248 of rectangular cross-section is provided through mandrel 218to permit the passage of the metal core 240. r

The shaper 202 has a continuous inner wall 231, the use of vacuum notbeing provided in this example, and said wall 231 is surrounded directlyby a cooling jacket 235 provided with water inlet and outlet pipes 236and 237, respectively.

The extrusion of the composite section to be obtained is carried out asin the preceding example with the sole difference that the metal core240 is passed through mandrel 218, and is driven during expansion by theconventional drawing crawler, which is also provided in this case andhas not been illustrated.

The expansible plastics material processed in accordance with theinvention may be of any known type, for example based either onpolystyrene as previously mentioned above, or based on high or lowdensity polyethylene, polyvinyl chloride (P.V.C.),acrylonitrilebutadiene-styrene (A.B.S.), A.B.S. P.V.C. mixtures,polyamides, polycarbonates, or any other materials having similar bases.The invention is however applicable in a particularly advantageousmanner to the production of sections of the expanded material disclosedin French Patent No. 1,225,499.

The following, non limitative examples illustrate the practicalperformance of the invention.

EXAMPLE 1 For the purpose of producing a cylindrical rod, there wasextruded a mixture based on polystyrene and expanding agent, having thefollowing composition:

Polystyrene beads parts by weight Sodium bicarbonate 3 parts by weight-The extrusion was effected in a single-worm extruder having a diameterof 40 mm and a length of 20 diameters, the compression rate of the wormbeing 2.4 The extruder was provided with a circular die of a diameter of31.2mm, in the axis of which there was held a solid mandrel having anoutside diameter of 25 mm, while a cylindrical shaper having an insidediameter of 32 mm and a length of 25 cm was disposed directly at theoutlet of the die and co-axially with the latter. The temperatures inthe extruder, from the hopper to the die, were as follows: l20l30-l30l50l 30l 20C. The worm was rotated at the rate of 25 revolutions perminute, and the extruded product was extracted with the aid ofa drawingcaterpillar at a speed of 0.35 metre per minute. The shaper was cooledby circulating water at ordinary temperature.

A solid cylindrical rod of a diameter of 32 mm, having a smooth,hard,'and waterproof outer skin was obtained in this manner. The sectionof the rod was constant. Its density was about 0.5 to 0.6. The outputwas about kilograms per hour.

EXAMPLE II The following mixture was extruded to obtain a cylindricalrod: a. Standard polystyrene beads (available commercially under thetrade name Lorkalene, quality 8)-l00 parts by weight Sodium bicarbonate5 parts by weight Vaseline Oil O.l parts by weight Stearic acid O.lparts by weight The mixture was homogenised for 3 minutes in a highspeed mixer.

b. Extrusion was carried out in a single-worm extruder 40 cm. indiameter and 20 diameters long, the compression ratio of the worm being2.5 The extruder was equipped, ahead of the die, with a sieve of 60mesh/sq.cm.

The extruder was also equipped with a circular die head 31.8 mm. indiameter on the axis of which was fixed a solid mandrel 27.2cm. inexternal diameter. A cylindrical shaper 25 cm. long was fixed adjacentthe outlet of the die and coaxially therewith. A conventionaldrawingcaterpillar was arranged at the outlet of the shaper.

c. The conditions of extrusion were as follows:

Temperatures of the body of the extruder, from the Temperatures of theextruder head and die: C

Worm: not cooled Body: cooled (by circulation of compressed air) speedof rotation of worm: 18 rpm;

Drawing speed of extruded rod: 27 cm/min.

. Shaper cooled by continuous circulation of water at I about 20C.

d. There was thus obtained a solid, rigid, and per- 5 fectly cylindricalrod 32 mm. in diameter, with a cellular internal structure and a smoothand glossy skin.

Its specific gravity was 0.57, corresponding to an output of 7.5kg/hour.

EXAMPLE Ill The following mixture was extruded to obtain a cylindricalrod: a. Small granules of impact polystyrene (available commerciallyunder the trade-name Lorkalene, impact quality 800) 100 parts by weightSodium bicarbonate parts by weight Vaseline oil 0.1 parts by weightStearic acid 0.1 parts by weight The composition was homogenised for 3minutes in a high-speed mixer.

b. Extrusion was carried out with the same machine as described inparagraph (b) of Example 11.

c. The conditions of extrusion were as follows:

Temperatures of the extruder body from the hopper to the head:l-140140-165C.

Head temperature: 125C Die temperature: 120C worm not cooled.

Body cooled by circulation of compressed air.

Speed of rotation of worm 17 rpm.

Drawing speed of rod extruded 19.5 cm/min.

Shaper cooled by circulation of water at about 20C.

d. There was thus obtained a solid, rigid, perfectly cylindrical rod 32mm. in diameter, with a cellular internal structure and asmooth-surfaced skin.

The specific gravity was 0.65, corresponding to an output of 6.5kg/hour.

EXAMPLE IV The following mixture was extruded to obtain a cylindricalrod a. Small granules of styrene-acrylonitrile copolymer (SAN)(commercially available under the tradename Dikaryl) 100 parts by weightSodium bicarbonate 3 parts by weight Vaseline oil 0.1 parts by weightStearic acid 0.1 parts by weight The composition was homogenised for 3minutes in a high-speed mixer.

The material was dried for 2 hours at 80C.

b. Extrusion was carried out with the apparatus described in paragraph(b) of Example 11. c. The conditions of extrusion were as followsTemperature of the body of the extruder from the hopper to the head 130135 140 140C.

Head temperature 130C.

Die temperature 125C Extruder worm not cooled.'

Extruder body cooled by circulation of compressed air.

Speed of rotation of worm E 20 rpm.

Speed of extrusion of rod 27 cm/min.

Shaper cooled by continuous circulation of water at about 20C. i

d. There was thus obtained a solid, rigid, and perfectly cylindrical rod32 mm. in diameter, with a cellular internal structure and a smooth andglossy surface.

The specific gravity was 0.55, corresponding to an output of 7.5kg./hour.

EXAMPLE V The following mixture was extruded to obtain a cylindrical roda. Small granules of acrylonitrile-butadiene styrenecopolymer (ABS)(available commercially under the trade-name Lorkaril, quality JA) partsby weight Sodium bicarbonate 3 parts by weight Vaseline oil 0.1 parts byweight Stearic acid 0.1 parts by weight The composition was homogenisedfor 3 minutes in a high-speed mixer.

The material was dried for 3 hours at 80C. b. Extrusion was carried outwith the apparatus described in paragraph (b) of Example 11. c. Theextrusion conditions were as follows Temperatures of the body of theextruder from the hopper to the head 140 C. Head temperature 135C. I Dietemperature 125C Worm not cooled. Body cooled by circulation ofcompressed air. Speed of rotation of worm 28 rpm. Extrusion rate of rod31 cm/min. Shaper cooled by continuous circulation of water at about20C. d. There was thus obtained a solid, fairly rigid, and perfectlycylindrical rod, 32 mm. in diameter, with a cellular internal structureand a skin with a smooth and glossy surface.

its specific gravity was 0.65, corresponding to an output of 10 kg/hour.

EXAMPLE VI The following mixture (ABS PVC) was extruded to obtain acoloured lightened rod afPVC powder (trade-name Ekavyl SDF 58)65 partsby weight ABS powder (trade-name Lorkaril (.ISR)) 25 parts by weightK120N (PMMA) powder 15 parts by weight Barium-cadmium salt stabilisersMark WS 4 parts by weight Mark C 2 parts by weight Calcium stearate 0.5parts by weight Lubricant Wax E. 0.2 part by weight Tixol ex (Silica)0.5 parts by weight Sodium bicarbonate 6 parts by weight Colouringagents Titanium oxide RLS 1.5 parts by weight Neospectra black 0.0617parts by weight Ultramarine blue 0.045 parts by weight Red F6 78160.0009 parts by weight The composition was homogenised for about 10minutes in a hi'gh-speedmixer. The material (ABS only) was previouslydried for 2 hours at 80C.

b. Extrusion was carried out with the apparatus described in paragraph(b) of Example I1.v c. The extrusionconditions were as followsTemperatures of the extruder body from the hopper to the head 130 140140 C. Head temperature 130C. Die temperature 125C Worm cooled by water.Body cooled by circulation of compressed air. Speed of rotation of worm5 3 rpm. Rate of extrusion of rod 25 cm/min. Shaper cooled by gentlecirculation of water at about 40C. d. There was thus obtained a solid,rigid, and perfectly cylindrical rod 32 mm. in diameter, with a cellularinternal structure and a skin with a smooth and very EXAMPLE VI] blend)at 140C in a high-speed mixer.

b. Extrusion was carried out with the machine described in paragraph (b)of Example H.

c. The extrusion conditions were as follows Temperatures of the extruderbody from the hopper to the head: 135 145 165 175C. Head temperature135C. Die temperature 120C. Worm cooled by water. Body not cooled.Rotation speed of worm 49 rpm. Extrusion rate of rod cm/min. Shapercooled by gentle continuous circulation of water at about 40C. I d.There was thus obtained a solid perfectly cylindrical rod, 32 mm. indiameter, with a cellular internal structure and a skin with a smoothand glossy surface.

its specific gravity was 0.82, corresponding to an output of 7.5kg/hour.

EXAMPLE VIII The following mixture (rigid PVC) was extruded to obtain acylindrical rod a. PVC powder Ekavyl (SDF 52) 80 parts by weight I K120Npowder-(PMMA) 20 parts by weight Barium-cadmium stabilising salts MarkWS 4 parts by weight Mark C 2 parts by weight Calcium stearate 0.5 partsby weight Lubricant wax powder E 0.2 parts by weight Tixolex (silica)0.5 parts by weight Sodium bicarbonate 6 parts by weight The compositionwas rendered homogeneous by treatment for about lOminutes in ahigh-speed mixer.

b. The extrusion was carried out in the apparatus described in paragraph(b)of Example 11.

c. The extrusion conditions were as follows Temperatures of the extruderbody form the hopper to the head 140 155 165 l85C. Head temperature137C. Die temperature 130C. Worm not cooled Body not cooled Speed ofrotation of worm 24 rpm. Rate of extrusion of rod 29.5 cm/min.

Shaper cooled by gentle continuous circulation of water at about 40C.

d. There was obtained a perfectly cylindrical solid rod, with a cellularinternal structure and a skin with a smooth and glossy surface.

lts specific gravity was 0.75, corresponding to an output of 10.700kg/hour.

EXAMPLE 1X The following mixture was extruded to obtain a cylindricalrod a. Polymethylmethacrylate beads (available under the trade-name ofAltulite quality MBP) 100 parts by weight Sodium bicarbonate 5 parts byweight Vaseline oil 0.05 parts by weight The composition was renderedhomogeneous by treatment for 3 minutes in a high-speed mixer.

b. Extrusion was carried out with the apparatus described in paragraph(b) of Example II. c. The extrusion conditions were as followsTemperatures of extruder body from the hopper to the head: 125 145 150155C.

Head temperature 140C.

Die temperature 130C.

Worm not cooled;

Body cooled by circulation of compressed air;

Speed of rotation of worm 24 rpm.

Extrusion rate of rod 23cm/min.

Shaper cooled by gentle continuous circulation of water at about 35C.

d. There was thus obtained a solid perfectly cylindrical rod 32 mm. indiameter with a cellular internal structure, and a skin with a fairlysmooth surface, which however, had a matt appearance.

EXAMPLE X The following mixture was extruded to obtain a cylindrical roda. Polyamide 11 granules (available commercially under the trade-nameRilsan, quality BES-HV.O) 100 parts by weight Vaseline oil 0.05 parts byweight Sodium bicarbonate 1 parts by weight The composition was renderedhomogeneous by treatment for about 3 minutes in a high-speed mixer. b.Extrusion was carried out with the apparatus described in paragraph (b)of Example 11. An insulating joint of Teflon (PTFE) was inserted betweenthe parts denoted by 4 and 7 in FIG. 1. c. The extrusion conditions wereas follows Temperatures of the extruder body from the hopper to the head160 C.

Head temperature 160C.

Die temperature C.

Body and worm not cooled Speed of rotation of worm 24 rpm.

Extrusion rate of product 34cm/min.

Shaper cooled by gentle continuous circulation of water at about 40C.

'd. There was thus obtained a solid perfectly cylindrical rod 31 mm. indiameter, with a cellular internal structure and a skin with a fairlysmooth and slightly glossy surface.

The specific gravity was 0.51, corresponding to an output of 8.300kg/hour.

EXAMPLE xx The composition was homogenised by treatment for 1 about 3minutes in a high-speed mixer.

b. Extrusion was carried out with the apparatus described in paragraph(b) of Example 11.

c. The extrusion conditions were as follows:

Temperatures of the extruder body from the hopper to the head: 135 150155 180C.

Head temperature 135C.

Die temperature 130C.

Body and worm not cooled.

Speed of rotation of worm 35 rpm.

Extrusion rate of rod 33.5 cm/min.

Shaper cooled by gentle continuous circulation of water at about 45C.

d. There was thus obtained a solid perfectly cylindrical rod 32 mm. indiameter, with a cellular internal structure, and having a skin with asmooth glossy surface. It was fairly rigid and its specific gravity was0.55, corresponding to an output of 8.800 kg/hour.

EXAMPLE XII The following mixture was extruded to obtain a cylindricalrod i a. High pressure polyethylene (commercially available under thetrade-name Plastylene PA 0234, powder, grade 1.8): 100 parts by weight IHigh pressure polyethylene (commercially available under the trade-nameLupolen 1800 H, granules, grade about 1.8): 20 parts by weight Sodiumbicarbonate 3 parts by weight Two types of polyethylene, one powderedand the other granulated, were used to facilitate feed of the extruder.

The composition was homogenised by treatment for about 5 minutes in ahigh-speed mixer.

b. Extrusion was carried out with the apparatus described in paragraph(b) of Example II.

c. The extrusion conditions were as follows Temperatures of extruderbody from the hopper to the head: 125- 135- 145 145C.

Head and die temperatures: 130C.

Worm and body not cooled;

Rotation speed of worm 24 rpm.

Drawing speed of rod 21 cm/min.

Shaper cooled by continuous circulation of water to about 20C.

(I. There was thus obtained a solid perfectly cylindrical rod, 32 mm. indiameter, with a cellular internal structure and a skin with a smoothsurface. Its specific gravity was 0.5, corresponding to an output of 5kg/hour. I

When the drawing speed of the profiled product was increased to 31cm/min. there was obtained a solid rod with a specific gravity of 0.32.

The cellular structure of the product did not preclude a certainflexibility. Thus, it was possible to form without breakage a circle ofabout 30 cm. in diameter from the rod of specific gravity 0.32, whichreturned to its former straight shape. A piece of rod 50 cm. long waseasily twisted through without visible change.

EXAMPLE XIII The following mixture was extruded to obtain a cylindricalrod a. Polypropylene powder (commercially available under the trade-namePrylene ML 0622, grade 18): parts by weight Azodicarbonamide powder(ADCM supplied by Bayer) 1 parts by weight Vaseline oil 0.05 parts byweight The composition was homogenised by treatment for about 5 minutesin a high-speed mixer.

b. Extrusion was carried out with the apparatus described in paragraph(b) of Example II. An insulating joint of Teflon was placed between theparts denoted by 4 and 7 in FIG. 1.

cfThe extrusion conditions were as follows Temperatures of the body ofthe extruder from the hopper to the head C.

Head temperature 145C.

Die temperature 135C.

Worm and body not cooled.

Speed of rotation of worm 52 rpm.

Drawing speed of extruded rod 27.5cm/min.

Shaper cooled by gentle continuous circulation of water at about 50C.

d. There was thus obtained a perfectly cylindrical solid rod 32 mm. indiameter, having a cellular internal structure and a skin with a fairlysmooth and slightly glossy surface. Its specific gravity was 0.56,corresponding to an output of 7.200 kg/hour.

EXAMPLE XIV The following mixture was extruded to obtain a cylindricalrod a. Small polycarbonate granules (commercially available under thetrade-name Makrolon type): 100 parts by weight K3200 Azodicarbonamidepowder (ADCM supplied by Bayer) 1 parts by weight Vaseline oil 0.05parts by weight The composition was homogenised by treatment for about 3minutes in a high-speed mixer.

The material was previously dried for 3 hours at 100C.

b. Extrusion was carried out with the apparatus described in paragraph(b) of Example 11.

c. The extrusion conditions were as follows:

Temperatures of the extruder body from the hopper to the head 190 205210C.

Head temperature 190C.

Die temperature 185C.

Worm and body not cooled Speed of rotation of worm 29 rpm.

Drawing speed of extruded rod 16.5 cm/min.

Shaper cooled by continuous circulation of water to about 25C.

d. There was obtained a solid cylindrical rod 32 mm. in diameter, with acellular internal structure, and a skin with a fairly smooth surface andslightly marbled matt appearance. Its specific gravity was 0.65,corresponding to an output of 5.200 kg/hour.

EXAMPLE XV The following mixture was extruded to obtain a cylindricalrod a. Small cellulose propionate granules (commercially available underthe trade-name Cellidor type CPI-l): 100 parts by weightAzidocarbonamide powder (ADCM supplied by Bayer): 0.5 parts by weight IVaseline oil 0.05 parts by weight The composition was homogenised bytreatment for about 3 minutes in a high-speed mixer.

The material had previously been dried for 2 hours at.70C.

b. The extrusion was carried out in the apparatus described in paragraph(b) of Example II. A Teflon insulating joint was placed between theparts denoted by 4 and 7 in FIG. 1.

c. The extrusion conditions were as follows Temperatures of the body ofthe extruder from the hopper to the head 135 170 4 180 200C.

Head temperature: 170C.

Die temperature 160C.

Worm and body not cooled Rotation speed of worm 17 rpm.

Drawing speed of extruded rod 23 cm/min.

Shaper cooled by gentle continuous circulation of water to about 40C.

d. There was thus obtained a solid perfectly cylindrical rod 32 mm. indiameter, with a cellular internal structure and a skin with a smoothsurface of a slightly marbled matt appearance. Its specific gravity was0.65, corresponding to an output of 7.2 kg/hour.

EXAMPLE XVI The following mixture was extruded to obtain a product ofrectangular cross-section a. (Same composition as described in paragraph(a) of Example 11 (standard polystyrene) and prepared under the sameconditions).

b. Extrusion was carried out in a single-worm extruder 45 mm. indiameter and 20 diameters in length, the compression ratio of the wormbeing 2.2. The extruder was equipped with a sieve of mesh/cm in front ofthe die.

The extruder'was also equipped with a head having a rectangular die withan internal size of 33 X 23 mm., in the axis of which was fixed andcarefully centred a solid rectangular mandrel measuring 29 X 19 mm.

A shaper with a rectangular passage measuring 33 X 20 mm. and cm. longwas arranged adjacent the die outlet and coaxially therewith.A'conventional drawing-caterpillar was situated at the outlet of theshaper.

c. The extrusion conditions were as follows Temperature of the extruderbody from the hopper to the head C.

Head temperature 130C.

Die temperature 125C.

Worm not cooled.

Body cooled by circulation of compressed air;

Speed of rotation of worm 13 rpm.

Drawing speed of rectangular product 35 cm/min.

Shaper cooled by continuous circulation of water to about 20C d. Therewas thus obtained a solid rectangular'profiled product measuring 33 X 23cm. in cross-section,

and with a cellular internal structure and a skin having a smoothsurface, slightly glossy and slightly fibrous in appearance. Itsspecific gravity was 0.4, corresponding to an output of 6.400 kg/hour.

EXAMPLE XVII The following mixture was extruded to obtain a cylindricalprofiled product with a toothed surface a. (Same composition asdescribed in paragraph (a) of Example I (standard polystyrene) andprepared under the same conditions).

b. The extrusion was carried out in a single-wormed extruder 60 cm. indiameter and 20 diameters in length, the compression ratio of the wormbeing 2.4 and no sieve being incorporated before the die. The extruderwas equipped with a head, of which the die had the shape of a toothedwheel 24 mm. in diameter (60 small deep teeth per 0.5mm). On the axis ofthe die was fixed a solid mandrel 20 mm. in circular exterior diameter.A cylindrical shaper 24 mm. in diameter and 30 cm. long was placed 1 mm.from the die and coaxially with it. A conventional drawing caterpillarwas arranged at the outlet of the shaper.

C. The extrusion conditions were as follows Temperatures of the body ofthe extruder, from the ameter, having on its external surface very smallmutually parallel grooves. These, which prevented the surface of theskin being perfectly smooth, endowed it with a non-slip surface. Itsspecific gravity was 0.38, corresponding to an output of 7.500 kg/hour.

EXAMPLE XVIII The following mixture was extruded to produce acylindrical profiled product with a smooth surface and the appearance ofinternal fibres a. Same extrusion composition as described in paragraph(a) of Example ll (standard polystyrene), prepared under the sameconditions.

1). The extrusion was carried out with the apparatus described inparagraph (b) of Example XVll. The shaper was kept in contact with thedie and coaxially therewith.

c. The extrusion conditions were those given in paragraph (c) of ExampleXVII, the drawing speed being 65 cm/minute.

d. There was thus obtained a solid perfectly cylindrical rod 24 mm. indiameter, with a cellular internal structure and a smooth-surfaced skinwithout external serration. The product thus had a surface which had theappearance of a fibrous nature, the fibres being due to the flatteningof the small serrations by contact with the shaper. The specific gravityof the rod obtained was 0.43, corresponding to an output of 7.500kg/hour.

EXAMPLE XlX The following mixture was extruded to obtain a cylindricalprofiledproduct, alternately hollow and solid a. Same composition asdescribed in paragraph (a) of example 11 (standard polystyrene).

b. Extrusion was carried out with the apparatus described in paragraph(b) of Example 11.

c. The extrusion conditions were as follows Temperatures of the extruderbody from the hopper to the head 120 140 140 150C.

Head temperature 120C.

Die temperature 115C.

Body cooled by circulation of compressed air.

Shaper cooled by continuous circulation of water to about 20C.

The above composition was extruded for 4 hours, the following cycle ofdrawing speeds being used 22cm/min. for 60 seconds;

38cm/min. for 120 seconds;

22cm/min. for 60 seconds;

38 cm/min. for 120 seconds; etc.

d. There was thus obtained a perfectly cylindrical rod (FIG. 13) 32 mm.in diameter with a hard, smooth, and compact external wall. This rodhad, roughly every 1,000 mm., solid cellular sections of average length200 mm. and specific gravity 0.6, separated by a hollow section about800 mm. long and bounded by a smooth, compact, cellular outer wall, witha total thickness of 7 mm, this cellular outer wall being of specificgravity 0.55. The apparent specific gravity of the whole profiledproduct was 0.45.

By cutting the product at convenient points there were obtained pieces100 mm. long closed at each end for a length of 100 mm. and containing acentral hollow portion 800 mm. long. (FIG. 13). The output obtained was7 kg/hour.

EXAMPLE XX The following mixture was extruded to obtain an alternatelysolid and hollow cylindrical profiled product a. Same composition asthat described in paragraph a. of Example Xll (high pressurepolyethylene) b. Extrusion was carried out with the apparatus describedin paragraph (b) of Example 11.

I scribed in paragraph (b) of Example 11.

c. The extrusion conditions were the same as those EXAMPLE XXI a. Thefollowing mixture was extruded to obtain a cylindrical rod Small highpressure vulcanizable polyethylene granules (commercially availableunder the commercial c. The extrusion conditions were as followsTemperatures of the extruder body from the hopper to the head: 125C Headtemperature: C I

Die temperature: 110C Worm not cooled Body cooled by circulation ofcompressed air Speed of rotation of worm 24 rpm Extrusion rate of rod 28cm/min.

Shaper cooled by circulation of water at about 35C and under vacuo.

d. There was thus obtained a solid perfectly cylindrical rod 32 mm indiameter, with a cellular internal structure and having a smooth skin.Its specific gravity was 0.42 corresponding to an out put of 5.750kg/hour EXAMPLE XXII For the extrusion of a composite cylindrical rodcomprising an outer sheath of polyethylene and an internal cellularstructure of expanded polystyrene, use 'was made of the apparatusillustrated in FIG. 14, with the following dimensional characteristics.

The first extruder, connected to the connection 113 of the cross-head,had a diameter of 40 mm and a length of 20 diameters. The compressionrate of the worm was 3.

The second extruder, connected to the connection 123 of the cross-head,had a diameter of 60 mm and a length of 20 diameters. The compressionrate of the worm was 2.

The die 106 had a section with an internal diameter of 38 mm. The frontend 115 of the sleeve 110 had an external diameter of 36 mm and aninternal diameter of 32 mm. The diameter of the mandrel 118 was 25 mmand the inside diameter of the shaper was 38.2 mm, its length being 25cm.

The first extruder, for producing the sheath through the die section 116, was fed with low density polyethylene powder of the grade sold underthe commercial name Plastylene. The temperature read on the body of thisextruder, from inlet to outlet, were as follows 140 150 160- 160C. Thetemperature in the die section 116 formed between die 106 and the frontend 1 15 of sleeve 110 was maintened at 160C by resistor 129. g

Sodium bicarbonate NaI-ICO (expanding agent) 3 parts Stearic acid(lubricant) 0.2 parts.

From inlet to outlet the temperature in this extruder were 120 130 C.The temperature in the die section 126 formed between the front end 115of sleeve 1 10 and mandrel 118 was kept close to 120C by circulating oilat said temperature in mandrel 118.

- methacrylate of a thickness of 0.9 mm.

The speed of rotation of the worm of this extruder was 15 rpm.

The shaper was cooled by circulation of water at 18C and the vacuum pumpconnected to the evacuation pipe l34was put into operation.

A cylindrical rod of a diameter of 38 mm was thus obtained which had aninternal cellular structure of a diameter of 36 mm, specific gravity0.48 covered by a smooth, compact sheath of low density polyethylene ofa thickness of.l mm.

EXAMPLE XXIII For the extrusion of a composite cylindrical rodcomprising an external sheath of polymethyl methacrylate and an internalcellular structure based on polyvinyl chloride (PVC), use was made ofthe same apparatus as that described in Example XXII, with the soledifference that the compression rate of the worm of the sec ond extruderconnected to the connection 123 of the cross-head was 3 and the speed ofrotation of said worm was 25 rpm.

The first extruder, for the formation of the sheath through the diesection 116, was fed with the die of polymethyl methacrylate beads ofthe grade sold under the commercial name ALTULITE grade MBP. From inletto outlet the temperature in this extruder were 140 160- 170- 180C. Thetemperatures in the die section formed between the die 106 and the frontend 115 of sleeve 110 was kept at 160C by means of resistor 129.

The second extruder, for producing the internal cellular structure ofthe rod and delevering through the die section 126, was fed with thefollowing expansible composition the proportions being indicated inparts b weight r PVC powder (K value 58) (Ekavyl SDF 58) 80 Polyrnethylmethacrylate (PMMA) beads (K 12ON) Barium and cadmium salts Mark WS: 6Mark C: 2

Lubricant (wax E): 0.2

Tixolex (silica powder): 0.5

Sodium carbonate: 6

From inlet to outlet the temperatures in this extruder were 140 160 170180C. The temperature in the die section 126 formed between the frontend 115 of the sleeve 110 was kept at about 170C by circulating oil atsaid temperature in mandrel 118.The speed of rotation of the worm ofthis extruder was 13 rpm.

The shaper was cooled by circulating water at 18C, but the vacuum pumpwas not connected.

There was thus obtained a cylindrical rod of a diameter of 38 mmcomprising an internal cellular structure of a diameter of 36.2 mm,specific gravity 0.65, and covered by a smooth, compact sheath ofpolymethyl EXAMPLE XXIV A composite rectangular section (FIG. 16) wasextruded, comprising a core composed of a flat section 240 of aluminum,cross-section 80 X 100 mm, covered by a cellular structure 241 based ona acrylonitrilebutadienstyrene (ABS) and polyvinyl chloride (PVC)copolymer of a thickness of mm, which in turn was covered by a sheath242 of polypropylene of a thickness of 0.5 mm.

For this purpose, use was made of an apparatus of the type illustratedin FIG. 15, having the following dimensional characteristics.

The first extruder, connected to the connection 213 of the cross-head,had a diameter of 40 mm and a length of 20 diameters. The compressionrate of the screw was 2.5.

The second extruder, connected to the connection 223 of the cross-headhad a diameter of 60 mm and a length of 20 diameters. The compressionrate of the screw was 3.

The rectangular cross-sections of the die 206, of the front end 215 ofsleeve 210, and of mandrel 218, and the the dimensions of the shaperwere as follows Inside cross-section of die 206 101 X 31 mm Outsidecross-section of end 215 of sleeve 210 x 30 mm Inside cross-section ofend 215 of sleeve 210 96 X Outside cross-section of mandrel 218: 92 X 22mm Inside cross-section of mandrel 218: 80 X 10 mm Inside cross-sectionof shaper 101.2 X 31.2 mm

Length of shaper 250 mm The first extruder, for forming the sheaththrough die section 216, was fed with polypropylene sold under thecommercial name PRYLENE ML 0622, grade 18. The temperatures read on thebody of this extruder were, from inlet to outlet 160 175 180 185C. Thetemperature in the die section 216 formed between die 206 and the frontend 215 of sleeve 210 was kept at 190C by resistor 229. The speed ofrotation of the worm was 8 rpm.

The second extruder, for the production of the internal cellularstructure of the section and delivering through die section 226, was fedwith the following expansible composition, the proportions beingindicated in parts by weight.

PVC powder (K value 58, Ekavyl SDF) 65 ABS (Lorkaril .ISR) 25 PMMApowder (K N): 15

Barium and cadmium salts 6 Calcium stearate 0.5

Lubricant (wax E) 0.2

Nal-ICO 6 This composition had been homogeneized by passing for 10minutes through a high speed mixer, the temperature of the ABS powderhaving first been raised to 80C for 2 hours.

From inlet to outlet the temperatures in this extruder were C. Thetemperature in the die section 226 formed between the front end 215 ofsleeve 210 was kept close to 130C by resistors 245. The speed ofrotation of the worm of this extruder was 23 rpm.

The aluminum section was introduced through mandrel 218 and pushedprogressively at the beginning of the extrusion operation, after whichit was driven, with the entire extruded product, by the drawing crawlerarranged downstream of the shaper.

The specific gravity of the cellular structure 241 of the compositesection thus obtained was 0.70.

It will be understood that many modifications can be madeintheperformance of the invention described above, without departing fromthe spirit and scope of the following claims.

1 claim:

1. A method of producing a foamed extruded thermoplastic materialproduct, the thermoplastic material being selected from the groupconsisting of polystyrene, polyvinyl chloride, polyethylene,acrylonitrilebutadiene-styrene copolymers, polyamides, polycarbonates,polyurethanes, styrene-acrylonitrile copolymers, polymethylmethacrylate, polypropylene, cellulose propionate, and mixtures thereof,wherein the thermoplastic material with an expanding agent therein isextruded from a die outlet into and through a shaper, the shaper havingan internal solid surface defining a channel, the channel being disposedsubstantially coaxially with the die, and having an inlet and an outlet,the inlet edge of the shaper substantially coinciding with the outletedge of the die, the cross-sectional area of the shaper beingsubstantially larger than the crosssectional area of the die outlet,thereby providing a void in the channel for the expansion of thethermoplastic material, the channel outlet cross-section beingsubstantially that of the product required, and the channel havingsubstantially the same cross-sectional size and shape along its fulllength,

cooling the internal solid surface of the shaper to a temperature belowthe softening point of the thermoplastic material, extruding thefoamable thermoplastic material through the die outlet in the form ofatubular body with a hollow cavity therein and an external surfacethereon, the temperature of the thermoplastic material being in therange from 70 to 210C,

immediately contacting the external surface of the tubular body with thecooled internal solid surface of the shaper, thereby cooling rapidly theexternal surface of the extruded tubular body below the softening pointof the thermoplastic material to retard foaming of the extruded materialon the external surface and to form a thick skin of higher densitymaterial thereon, thereby imparting sufficient mechanical strength tothe extruded product in the shaper to permit it to be extruded throughthe shaper, and

expanding the extruded material forming the tubular body toward theinside of the channel to at least partially fill the hollow cavity ofthe tubular body.

2. The method of claim 1 wherein the cavity inside the extruded materialis produced by a mandrel coaxial with the die and disposed therein.

3. The method of claim 1 wherein the extruded material expands towardthe inside of the channel to fill the hollow cavity in every portion ofthe tubular body, whereby a solid extruded product is produced.

4. The method of claim 1 wherein the extruded material expands towardthe inside of the channel to fill the hollow cavity in at least twoportions of the tubular body, whereby an extruded product having atleast one hollow portion therein is produced.

5. The method of claim 1 wherein for a first period of time a solidproduct is produced, and for a second period of time a hollow product isproduced, the cycle being repeated at least once, whereby a producthaving alternate hollow and solid sections is produced.

6. The method of claim 1 wherein the inlet edge of the shaper channeldefines a cross-sectional area substantially the same size and shape asthe die section.

7. The method of claim 1 comprising the additional step of feeding theelongated core member in a continuous manner within said hollow cavityin said extruded tubular body during extrusion.

8. The method of claim 1 further comprising the step of pulling theextruded product through the shaper.

9. The ,method of claim 8 wherein the extruded product is pulled throughthe shaper by means of a drawing caterpillar, the drawing caterpillarbeing positioned downstream of the shaper and along the path of travelof the extruded product.

10. A method of producing a foamed extruded thermoplastic materialproduct, the thermoplastic material being selected from the groupconsisting of polystyrene, polyvinyl chloride, polyethylene,acrylonitrilebutadiene-styrene copolymer, polyamides, polycarbonates,polyurethanes, styrene-acrylonitrile copolymers, polymethylmethacrylate, polypropylene, cellulose propionate, and mixtures thereof,wherein the thermoplastic material with an expanding agent therein isextruded from a die outlet into and through a shaper, the shaper havingan internal solid surface defining a channel, the

channel having an inlet and an outlet, the inlet edge of the shaperchannel substantially coinciding with outlet edges of the die, thechannel area of the inlet circumscribing and being larger than the areaof the die outlet thereby forming a void in the channel for expansion ofthe thermoplastic material, the channel outlet crosssection beingsubstantially that of the product required, and the channel havingsubstantially the same crosssectional size and shape along its fulllength,

cooling the internal solid surface of the shaper to a temperature belowthe softening point of the thermoplastic material,

extruding the foamable thermoplastic material through the die outlet,the temperature of the thermoplastic material being in the range from to210C, the extruded material having an external surface thereon,

immediately contacting said external surface with the cooled internalsolid surface of the shaper, thereby cooling rapidly said externalsurface below the softening point of the thermoplastic material toretard foaming of the extruded material along the entire length of theextruded product and to form a thick skin of higher density. materialthereon, thereby forming a continuous area of thick skin on the externalsurface of the extruded product and imparting sufficient mechanicalstrength thereto in the shaper to permit it to be extruded through theshaper, and

expanding the extruded material from the external surface with the thickskin thereon toward the inside of the shaper channel tosubstantiallyfill the channel.

11. The method of claim 10 further comprising the step of pulling theextruded product through the shaper.

12. The method of claim 11 wherein the extruded product is pulledthrough the shaper by means of a drawing caterpillar, the drawingcaterpillar being positioned downstream of the shaper and along the pathof travel of the extruded product.

13. A method of producing a foamed extruded thermoplastic materialproduct, the thermoplastic material being selected from the groupconsisting of polystyrene, polyvinyl chloride, polyethylene,acrylonitrilebutadiene-styrene copolymers, polyamides, polycarbonates,polyurethanes, styrene-acrylonitrile copolymers, polymethylmethacrylate, polypropylene, cellulose propionate, and mixtures thereof,wherein the thermoplastic material with an expanding agent therein isextruded from a die outlet into and through a shaper,

the shaper having an internal solid surface defining a channel. thechannel having an inlet and outlet, the inlet perimeter of the shapersubstantially coinciding with outlet edges of the die for substantiallythe entire perimeter of the inlet of the shaper, the cross-sectionalarea of the shaper being substantially larger than the cross-sectionalarea of the die outlet, thereby providing a void in the channel for theexpansion of the thermoplastic material, the channel outletcross-section being substantially that of the product required, and thechannel having substantially the same cross-sectional size and shapealong its full length,

cooling the internal solid surface of the shaper to a temperature belowthe softening point of the thermoplastic material, extruding thefoamable thermoplastic material through the die outlet, the temperatureof the thermoplastic material being in the range from 70 to 28 2lOC,

immediately contacting the external surface of the extrudedthermoplastic material with the cooled internal solid surface of theshaper, thereby cooling rapidly the external surface of thethermoplastic material below the softening point of the thermoplasticmaterial to retard foaming of the extruded material on the externalsurface and to form a thick skin of higher density material thereon,thereby imparting sufficient mechanical strength to the extruded productin the shaper to permit it to be extruded through the shaper, and

expanding the extruded material toward the inside of the channel to atleast partially fill said void,

14. The method of claim 13 further comprising the step of pulling theextruded product through the shaper.

15. The method of claim 14 wherein the extruded product is pulledthrough the shaper by means of a drawing caterpillar.

2. The method of claim 1 wherein the cavity inside the extruded material is produced by a mandrel coaxial with the die and disposed therein.
 3. The method of claim 1 wherein the extruded material expands toward the inside of the channel to fill the hollow cavity in every portion of the tubular body, whereby a solid extruded product is produced.
 4. The method of claim 1 wherein the extruded material expands toward the inside of the channel to fill the hollow cavity in at least two portions of the tubular body, whereby an extruded product having at least one hollow portion therein is produced.
 5. The method of claim 1 wherein for a first period of time a solid product is produced, and for a second period of time a hollow product is produced, the cycle being repeated at least once, whereby a product having alternate hollow and solid sections is produced.
 6. The method of claim 1 wherein the inlet edge of the shaper channel defines a cross-sectional area substantially the same size and shape as the die section.
 7. The method of claim 1 comprising the additional step of feeding the elongated core member in a continuous manner within said hollow cavity in said extruded tubular body during extrusion.
 8. The method of claim 1 further comprising the step of pulling the extruded product through the shaper.
 9. The method of claim 8 wherein the extruded product is pulled through the shaper by means of a drawing caterpillar, the drawing caterpillar being positioned downstream of the shaper and along the path of travel of the extruded product.
 10. A method of producing a foamed extruded thermoplastic material product, the thermoplastic material being selected from the group consisting of polystyrene, polyvinyl chloride, polyethylene, acrylonitrile-butadiene-styrene copolymer, polyamides, polycarbonates, polyurethanes, styrene-acrylonitrile copolymers, polymethyl methacrylate, polyPropylene, cellulose propionate, and mixtures thereof, wherein the thermoplastic material with an expanding agent therein is extruded from a die outlet into and through a shaper, the shaper having an internal solid surface defining a channel, the channel having an inlet and an outlet, the inlet edge of the shaper channel substantially coinciding with outlet edges of the die, the channel area of the inlet circumscribing and being larger than the area of the die outlet thereby forming a void in the channel for expansion of the thermoplastic material, the channel outlet cross-section being substantially that of the product required, and the channel having substantially the same cross-sectional size and shape along its full length, cooling the internal solid surface of the shaper to a temperature below the softening point of the thermoplastic material, extruding the foamable thermoplastic material through the die outlet, the temperature of the thermoplastic material being in the range from 70* to 210*C, the extruded material having an external surface thereon, immediately contacting said external surface with the cooled internal solid surface of the shaper, thereby cooling rapidly said external surface below the softening point of the thermoplastic material to retard foaming of the extruded material along the entire length of the extruded product and to form a thick skin of higher density material thereon, thereby forming a continuous area of thick skin on the external surface of the extruded product and imparting sufficient mechanical strength thereto in the shaper to permit it to be extruded through the shaper, and expanding the extruded material from the external surface with the thick skin thereon toward the inside of the shaper channel to substantially fill the channel.
 11. The method of claim 10 further comprising the step of pulling the extruded product through the shaper.
 12. The method of claim 11 wherein the extruded product is pulled through the shaper by means of a drawing caterpillar, the drawing caterpillar being positioned downstream of the shaper and along the path of travel of the extruded product.
 13. A method of producing a foamed extruded thermoplastic material product, the thermoplastic material being selected from the group consisting of polystyrene, polyvinyl chloride, polyethylene, acrylonitrile-butadiene-styrene copolymers, polyamides, polycarbonates, polyurethanes, styrene-acrylonitrile copolymers, polymethyl methacrylate, polypropylene, cellulose propionate, and mixtures thereof, wherein the thermoplastic material with an expanding agent therein is extruded from a die outlet into and through a shaper, the shaper having an internal solid surface defining a channel, the channel having an inlet and outlet, the inlet perimeter of the shaper substantially coinciding with outlet edges of the die for substantially the entire perimeter of the inlet of the shaper, the cross-sectional area of the shaper being substantially larger than the cross-sectional area of the die outlet, thereby providing a void in the channel for the expansion of the thermoplastic material, the channel outlet cross-section being substantially that of the product required, and the channel having substantially the same cross-sectional size and shape along its full length, cooling the internal solid surface of the shaper to a temperature below the softening point of the thermoplastic material, extruding the foamable thermoplastic material through the die outlet, the temperature of the thermoplastic material being in the range from 70* to 210*C, immediately contacting the external surface of the extruded thermoplastic material with the cooled internal solid surface of the shaper, thereby cooling rapidly the external surface of the thermoplastic material below the softening point of the thermoplastic material to retard foaming of the extruded material on the external surface and to form a thick skin of higHer density material thereon, thereby imparting sufficient mechanical strength to the extruded product in the shaper to permit it to be extruded through the shaper, and expanding the extruded material toward the inside of the channel to at least partially fill said void.
 14. The method of claim 13 further comprising the step of pulling the extruded product through the shaper.
 15. The method of claim 14 wherein the extruded product is pulled through the shaper by means of a drawing caterpillar. 